This invention relates generally to means for closing and locking the movable die of an injection molding apparatus, the movable die being operated by a piston and cylinder unit and being locked upon application of pressure to a die locking chamber after the movable die is closed.
Known injection molding apparatus have a pair of matching dies, one of which being mounted on a stationary die plate and the other mounted on a sliding die plate. The sliding die plate is guided on rails or rods, and the piston of a pressurized piston and cylinder unit is connected thereto for opening and closing the movable die as quickly as possible. And, since the material injected into the die exerts considerable pressure on the die plates, tending to open them after closing, an appropriate die locking force must be exerted on the movable die. Die locking hydraulic cylinders are typically provided for this purpose. Thus, the two functions, namely, the sliding of the die and the locking of the die has heretofore been carried out separately, as set forth in West German Pat. Nos. 2,453,697 and 1,268,322.
Since the piston for closing and opening the die must operate at a relatively low pressure, and since the die locking cylinder must normally be pressurized with considerable locking pressure, a substantial amount of hydraulic working fluid had to be utilized in the past.